It is a desired feature in most homes and in many business to have at least one lighting fixture in which the intensity of the light generated by the fixture is controllable over a range of illumination. For example, many lamps include so-called trilight switches and a special light socket which allows the use of a special two-filament bulb to achieve three levels of illumination. In a different manner, overhead lighting fixtures, such as chandeliers and the like, are often connected to a wall mounted dimmer mechanism which allows the illumination produced by the overhead fixture to be varied over a wide range. Typically, the wall mounted dimmer control comprises a potentiometer which controls the phase angle of the a.c. power applied to the incandescent bulb or bulbs in the overhead fixture. Typically, the dimmer control includes a triac which is responsive to the phase angle control of an resistancecapacitance network that includes the potentiometer to thereby allow current to flow through the incandescent bulb during only a portion of each half-cycle of the a.c source.
Both the trilight switch in the lamp and the potentiometer controlled dimmer control in the wall are mechanical devices which suffer from failures after extended use. Furthermore, both devices require manual manipulation of the controls, and, in the case of persons having arthritis or other disabilities, are difficult to operate. Thus, a need has existed for devices to replace both types of lighting controls. In the case of the lamps, a number of devices have become available in the art to control the intensity of the incandescent bulbs in lamps. For example, U.S. Pat. No. 3,715,623 to Szabo teaches the basic principal of phase control of an incandescent bulb responsive to touch activation. Similarly, U.S. Pat. No. 4,119,864 to Petrizio teaches another version of a touch control circuit having additional levels of illumination. U.S. Pat. No. 3,805,096 to Hamilton discloses an alternative embodiment of a touch control circuit having on-off control as well as level control. Other circuits for controlling the intensity of incandescent bulbs are known. For example, LSI Computer Systems, Inc., Melville, N.Y., manufactures and sells a series of brightness control integrated circuits.
Although each of the foregoing prior art devices are electrically capable of providing touch-control of the brightness of an incandescent bulb, the circuits are not mechanically suitable for many applications. For example, in order to be approved by Underwriters Laboratories, any wall-mounted switch must include a means for positively disconnecting the a.c. power from the incandescent bulb. One cannot simply rely upon the on-off state of the touch control circuit described above. Thus, an air-gap switch must be provided in addition to the touch control circuit in order to meet the Underwriters Laboratories' requirements. (An air-gap switch is one having metallic electrical contacts which are separated by air or another insulating medium when the switch is its off position.)
There are presently a small number of lighting control devices available which provide touch control and also include an air-gap switch to meet the Underwriters Laboratories' requirements. However, the only switches presently available have peculiar mounting requirements which prevent them from being used as direct replacements for a standard wall-mounted on-off toggle switch. For example, Leviton Manufacturing Company, Inc. sells a touch dimmer which must be installed with a special wall plate having an opening having dimensions of approximately 2.6 inches by 1.3 inches, in contrast to the standard toggle switch opening of approximately 1 inch by 0.4 inches. Thus, in order to install the touch control dimmer from Leviton, a special wall plate must be purchased. If the touch control switch from Leviton is to be installed along side other standard switches, a special wall plate having an enlarged opening for the touch control switch and standard size openings for the normal switches must be purchased. One can readily see that a large number of specialized wall plates must be provided to provide the capability of installing the dimmer switches in various combinations with the standard wall switches. Thus, a need exists for a touch-control wall dimmer switch which can be installed as a direct replacement for a standard toggle switch using the opening in a standard wall plate.